Auto-sync with upstream branch release/2.26/master
    
    Upstream commit: 174709d879a15590e00119c7f91dc2460aaf571c
    
    - CVE-2018-11237: Buffer overflow in mempcpy for Xeon Phi (#1581275)
    - nptl: Fix waiters-after-spinning case in pthread_cond_broadcast (#1622669)
    - x86: Correct index_cpu_LZCNT (swbz#23456)
    - x86: Populate COMMON_CPUID_INDEX_80000001 for Intel CPUs (swbz#23459)
    - stdio-common/tst-printf.c: Remove part under a non-free license (swbz#23363)
    - libio: Disable vtable validation in case of interposition (swbz#23313)
    - if_nametoindex: Check length of ifname before copying (swbz#22442)
    - getifaddrs: Don't return ifa entries with NULL names (swbz#21812)
    - time: Use _STRUCT_TIMESPEC as guard in <bits/types/struct_timespec.h>
      (swbz#23349)
    - math: Fix parameter type in C++ version of iseqsig (swbz#23171)
    - libio: Avoid _allocate_buffer, _free_buffer function pointers (swbz#23236)